The invention relates to a starter and power generator which starts an engine and which then generates power utilizing the drive from the engine, and a motor which may be used in such starter, and in particular, to a self-controlled commutatorless motor which produces a rotating magnetic field within a stator in accordance with an angle of rotation of a rotor.
An engine which is mounted on an automobile, for example, is provided with a starter for starting the operation of the engine as well as a power generation system which generates power during the rotation of the engine to charge a battery.
As is known, when the rotary shaft of a d.c. motor is rotated by an external drive, there may be obtained a d.c. output. Thus, a d.c. motor may be maintained in coupled relationship with an output shaft of an engine, thereby allowing the motor to operate as a d.c. generator ("dynamo") after the engine has started. In fact, there has been an arrangement referred to as a "starter dynamo" which combined a starter and a power generation system.
However, the use of a commutator in a dynamo has a drawback that it is not amenable to a high speed operation. Specifically, a pulley ratio (the ratio of numbers of revolutions between a generator and an engine) must be chosen so as to enable the operation of the dynamo when the engine operates at its maximum speed. This causes a difficulty that a battery may be discharged as a result of failure of providing sufficient power generation if an automobile which carries such dynamo is obliged to run at low speed over an increased length of time due to traffic stagnation. For this reason, an arrangement referred to as "starter dynamo" has disappeared, and has been replaced by a combination of an alternator of a reduced weight and size which is capable of providing a high output and serving as a power generator and a d.c. direct wound motor as a starter which provides a starting torque of an increased magnitude and allows a high speed rotation.
On the other hand, the recent trend toward the forward wheel drive of automobiles requires a greater reduction in the weight and size of as well as a higher output from an engine and installations thereon. Thus, the separate provision of the alternator as a power generator and a d.c. direct wound motor as a starter stands in the way to satisfy such requirement.